U.S. patent number 4,983,458 [Application Number 06/914,329] was granted by the patent office on 1991-01-08 for reflective particles.
This patent grant is currently assigned to Potters Industries, Inc.. Invention is credited to Robert Dejaiffe.
United States Patent |
4,983,458 |
Dejaiffe |
January 8, 1991 |
Reflective particles
Abstract
A reflective marker for highway striping, signs and other
surfaces is produced from a multiplicity of thermoplastic or
thermosetting granules in the shape of tetrahedrons. A plurality of
glass spheres having a diameter in the range of from about 6.0
microns to about 0.125 inches are substantially evenly dispersed
throughout each granule with some of the spheres protruding through
the outer granule surfaces. To form the granules the glass spheres,
the granule material and a suitable pigment are mixed together and
then applied to a flexible sheet or a roller containing a
multiplicity of tetrahedron-shaped indentations. The mixture is
urged into each of the indentations and is then cured. The
resulting granules are removed from the indentations and are
dropped from a random position onto a freshly painted highway line
or other surface such that one of the flat faces on each granule is
disposed in a downward direction. As the paint dries and hardens,
the granules are firmly held in place on the surface to provide a
reflective marker.
Inventors: |
Dejaiffe; Robert (Oak Ridge,
NJ) |
Assignee: |
Potters Industries, Inc.
(Parsippany, NJ)
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Family
ID: |
27096625 |
Appl.
No.: |
06/914,329 |
Filed: |
October 2, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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653943 |
Sep 21, 1984 |
|
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Current U.S.
Class: |
428/402; 359/540;
404/94; 428/143; 428/406; 428/407; 523/172; 523/219 |
Current CPC
Class: |
B29C
43/085 (20130101); B29D 11/00615 (20130101); E01C
7/35 (20130101); G02B 5/128 (20130101); E01F
9/524 (20160201); Y10T 428/2982 (20150115); Y10T
428/24372 (20150115); Y10T 428/2996 (20150115); Y10T
428/2998 (20150115) |
Current International
Class: |
B29C
43/08 (20060101); B29C 43/04 (20060101); B29D
11/00 (20060101); E01C 7/00 (20060101); E01F
9/04 (20060101); E01C 7/35 (20060101); G02B
5/12 (20060101); G02B 5/128 (20060101); G02B
005/128 (); E01C 023/16 (); F21V 007/22 (); C08J
009/32 () |
Field of
Search: |
;350/105
;404/17,22,71,93,94 ;428/325,357,402,406,407 ;523/172,219 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Van Balen; William J.
Attorney, Agent or Firm: Curtis, Morris & Safford
Parent Case Text
This application is a continuation of application Ser. No. 653,943,
filed Sept. 21, 1984.
Claims
What is claimed is:
1. A multiplicity of small reflective particles comprising
tetrahedron-shaped granules of plastic material, and a plurality of
glass spheres substantially evenly dispersed throughout each
granule with some of the spheres protruding through the outer
surface thereof, the proportion of said spheres to the granule
material being about 30 to 60 percent by weight for each granule,
each of the granules having a plurality of flat faces which meet at
an acute angle to form a straight abrupt edge, the granules being
of a size and shape such that when dropped from a random position
onto a horizontal tacky surface a flat face of all of the granules
sinks into said surface in facing contact therewith, the abrupt
edges of all of the granules forming wedges to hold the granules in
place on said surface.
Description
BACKGROUND OF THE INVENTION
This invention relates to reflective material and more particularly
to reflective particles used for reflective marking.
The present invention, while of general application, is
particularly well suited for use on highways to provide reflective
markers such as edge and lane striping, signs, etc. As is well
known, it has become common practice to drop small glass spheres
onto a painted line on a highway while the paint is still tacky
such that the spheres are partially imbedded in the paint when it
has dried. The spheres render the line or other marker
retroreflective and reflect the light from headlights so that the
marker is more visible to the motorist. In some cases the spheres
were imbedded in spherical or irregularly shaped plastic granules
prior to being applied to the paint in the manner disclosed in U.S.
Pat. Nos. 3,252,376 and 3,254,563, for example, in an effort to
further improve the reflectivity of the marker.
Heretofore, difficulties were encountered in the manufacture and
use of reflective material of the foregoing type. As an
illustration, in many instances the adhesion of the glass spheres
to the paint proved deficient, with the result that some of the
spheres were loosened by traffic or washed away druing rainstorms,
for example, with a corresponding deterioration in the reflectivity
of the surface. In addition, the spheres that remained were
subjected to severe abrasion under heavy traffic conditions and
exhibited flattened upper surfaces which further impaired the
reflectivity of the marker. Furthermore, and this has been of
special moment during periods of heavy rain, the reflectivity of
even freshly applied striping or other marking was deficient in a
number of respects.
SUMMARY
One general object of the invention, therefore, is to provide a new
and improved reflective particle for use in highway and other
reflective marking.
More specifically, it is an object of this invention to provide a
reflective particle that remains in place on a supporting surface
for an extended period of time.
A further object of the invention is to provide a reflective marker
which exhibits uniform and in some cases improved reflectivity
after long periods of use.
Still another object of the invention is to provide a reflective
marker which exhibits good reflectivity when in a wet or moistened
condition.
A still further object of the invention is to provide an improved
reflective marker which is economical and thoroughly reliable in
operation.
In one illustrative embodiment of the invention, the reflective
marker comprises a multiplicity of uniquely shaped granules of
plastic material. Imbedded in at least the exposed surfaces of the
granules are a plurality of glass spheres which protrude through
the surfaces to provide the granules with reflective
characteristics. For many applications the granules are dropped or
otherwise applied to a painted substrate with the paint in a tacky
condition, but in other cases the granules may be premixed with
paint and then applied to the substrate in a single operation.
In accordance with one feature of the invention, each of the
granules is provided with at least one flat face and is of a shape
such that when dropped from a random position onto a horizontal
surface the flat face is disposed in a downward direction. The flat
face is imbedded in the layer of paint to provide optimum adhesion
of the granule to the surface.
In accordance with another feature of the invention, in certain
particularly important embodiments, each granule is in the shape of
a tetrahedron. The tetrahedrons preferably are of a shape such that
when sprinkled from a random position onto a painted line of a
highway, for example, one of the faces of the tetrahedron is
disposed downwardly and the remaining faces meet the downward face
at an angle of about seventy degrees. With this arrangement the
resulting marker exhibits high reflectivity with respect to the
headlights of a vehicle particularly under wet conditions.
In accordance with a further feature of several advantageous
embodiments of the invention, the maximum height of the plastic
granules above the surface lies within the range of from about 2
millimeters to about 12 millimeters, and the granules are of at
least two distinct sizes. The larger size granules become flattened
by traffic to expose a greater quantity of the glass spheres
imbedded therein, while the smaller granules retain their
tetrahedron shape for an extended period of time. The arrangement
is such that the reflectivity of the marker remains substantially
uniform and in some cases increases during long periods of use.
In accordance with still another feature of the invention, in
several good arrangements, the granules are formed by advancing a
plastic sheet in a softened condition over a roller containing a
multiplicity of tetrahedron-shaped indentations to individually
mold each granule. The glass spheres are applied to the sheet prior
to the molding operation by spraying the spheres onto the flat
surfaces of the sheet and in some cases by mixing additional
spheres with the plastic material used to form the sheet. The size
and shape of each individual granule is determined by the
configuration of the indentations in the roller to provide a very
precise control over the reflectivity characteristics of the
resulting marker.
The present invention, as well as further objects and features
thereof, will be more fully understood from the following
description of certain preferred embodiments, when read with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a substantially enlarged perspective view of a molded
tetrahedron-shaped granule containing glass spheres in accordance
with an illustrative embodiment of the invention.
FIG. 2 is a vertical sectional view taken along the line 2--2 in
FIG. 1.
FIG. 3 is an enlarged side elevational view of a portion of a
roadway having a reflective marker which includes different size
granules of the type illustrated in FIG. 1.
FIG. 4 is a vertical sectional view of the roadway portion of FIG.
3.
FIG. 5 is a vertical sectional view similar to FIG. 4 but showing
the reflective marker after it has been subjected to heavy
traffic.
FIG. 6 is a perspective view with a portion shown in section of a
thermoplastic sheet used in the manufacture of the granules.
FIG. 7 is a prespective view of the thermoplastic sheet of FIG. 6
during the application of glass spheres to its exposed
surfaces.
FIG. 8 is a partially schematic front elevational view of the
thermoplastic sheet as it is advanced between rollers to form the
granules.
FIG. 9 is a partially schematic side elevational view of the
rollers and associated components illustrated in FIG. 8.
DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
Referring to FIGS. 1 and 2 of the drawings, there is shown a small
reflective particle in the form of a plastic resin granule 20. The
granule 20 has at least one flat face 22 and is of a shape such
that when dropped from a random position onto a horizontal surface
the face 22 is disposed in a downward direction, for purposes that
will become more fully apparent hereinafter. Advantageously the
granule 20 is in the form of a tetrahedron and in addition to the
downward face 22 has additional faces 23, 24 and 25. For granules
in the shape of an equilateral tetrahedron the angle .theta.
between the face 22 and the adjoining faces 23, 24 and 25 is
60.degree.. Particularly good results are achieved with granules
having an angle .theta. of at least 60.degree. and preferably about
70.degree..
Evenly dispersed throughout the granule 20 are a multiplicity of
glass beads or spheres 27. Some of the spheres 27 protrude through
the faces 22, 23, 24 and 25 of the granule 20 and similarly are
evenly dispersed through the surface area of each face. The spheres
27 are of a type commonly used in reflective marking and have a
diameter in the range of from about 6.0 microns to about 0.125
inches depending upon the particular type of reflective marker with
which the spheres are to be used. For best results the spheres 27
should have an index of refraction of at least about 1.5, and in
situations where particularly good retroreflectivity is desired the
refractive index of the spheres may be up to about 2.0. In some
cases a reflective coating such as a silver may be applied to the
spheres which provides even higher retroreflectivity for certain
applications. The spheres illustratively may be produced in the
manner disclosed in T. K. Wood U.S. Pat. No. 2,947,115, for
example, and for many applications they are provided with a
suitable coupling agent coating such as the silanes, titanates with
vinyl groups, terminal amines or epoxides. For a more detailed
discussion of representative coatings for the spheres, reference
may be had to James R. Ritter et al U.S. Pat. No. 3,867,178 .
The tetrahedron-shaped granules 20 containing the glass spheres 27
may be employed as illustrated in FIG. 3 to provide a reflective
marker on a surface 30 which illustratively comprises a roadway or
highway sign. A layer 31 of traffic paint of other adherent
material is first applied to the surface 30, and while the paint is
still tacky the granules 20 are dropped from a random position and
become imbedded in the paint. Because of their configuration the
granules 20 come to rest on the painted surface with one of their
flat faces 22 disposed in a downward direction irrespective of the
orientation of the granules at the time of their release. With this
arrangement the entire area of the face 22 on each granule is in
facing contact with the paint to provide extremely good adhesion
between the granules and the roadway surface. Each individual
granule is imbedded in the layer of paint, and the paint may
exhibit a slight wicking action to further help maintain the
granules in position and prevent any substantial quantity of
granules from becoming dislodged even under heavy traffic
conditions.
The size of the plastic granules 20 is carefully controlled such
that their height above the roadway surface 30 ranges between about
2 millimeters and about 12 millimeters. For granules having a
height much below 2 millimeters the quantity of glass spheres 27
within each granule is too small to provide a satisfactory
improvement in retroreflective properties, particularly during
rainy conditions, while for granules above about 12 millimeters in
height the surface becomes too rough and there is unnecessary
wastage of the granule material due to traffic wear, shearing by
snow plows, etc. In addition, the granules within this range
advantageously are divided into two and in some cases three
distinct sizes. As illustrated in FIGS. 3 and 4, for example, the
granules applied to the surface 20 comprises comparatively large
granules 20a which range in height from about 6 millimeters to
about 12 millimeters, medium-size granules 20b which range in
height from about 4 millimeters to about 6 millimeters, and small
granules 20c which range in height from about 2 millimeters to
about 4 millimeters. In cases in which only two size ranges are
used for the granules, the large granules have a height of between
about 5 millimeters and about 12 millimeters, and the small
granules have a height between about 2 millimeters and about 5
millimeters.
FIG. 5 is an illustration of the granule-coated roadway surface 30
after being subjected to abrasion by heavy traffic. The upper
portions of the large granules 20a and the medium-size granules 20b
have been eroded to provided flat horizontal surfaces 33, while the
upper portions of the small granules 20c have not been subjected to
abrasion and retain their original tetrahedron shapes. During the
erosion of the granules 20a and 20b the glass spheres 27 within the
interiors of the granules become exposed and protrude through the
upper surfaces 33 to help retain the optical properties of these
larger granules. In addition, the reflective angle .theta. (FIG. 2)
remains the same irrespective of the degree of erosion and
preferably is approximately 70.degree. to provide an optimum
reflective angle on a highway for the headlights of a vehicle. The
arrangement is such that the reflective marker retains good
retroreflective properties even after being exposed to long periods
of heavy traffic, and there is very little impairment of the
retroreflective properties during rainstorms and in other instances
where puddles are formed on the roadway. The flat surfaces 33 on
the larger granules 20a and 20b in many instances are disposed
above the puddles, and the glass spheres protruding therefrom
retain much of their retroreflective properties.
The material from which the granules 20 are formed may be selected
from a wide variety of thermoplastic and thermosetting resins.
Suitable thermoplastic resins include the polyolefins,
polyethylene, polypropylene, polymethyl methacrylate, acrylonitrile
butadiene styrene, etc., while the thermosetting resins that may be
used comprise the polyesters, urethanes, methyl methacrylate and
acrylonitrile. Substantially any thermoplastic or thermosetting
resin may be employed that exhibits good wear resistance and gives
off a minimum of volatile matter during curing.
The polyester resins, for example, in general comprise unsaturated
alkyd resins which are formed by the reaction of one or more
dicarboxylic acid components and one or more polyhydric alcohols.
Illustrative dicarboxylic acid components include saturated
anhydrides and adipic and azelaic acids, and the unsaturated
components fumaric acid and maleic acid. The commonly used dihydric
alcohols include glycols of ethylene propylene, 1, 3- and 2, 3-
butylene, diethylene and dipropylene. The polyester reaction
products are mixed with a nonvolatile unsaturated monomeric
cross-linking agent for the polyester resin such as a methyl
methacrylate. Other materials that may be employed as a monomeric
agent include styrene, vinyl toluene, vinyl acetate, ortho and para
methyl styrene, divinyl benzene, ethyl acrylate and many others.
The monomeric agent is of the nature such that it is consumed
during the curing of the resin without forming volatile
materials.
Still other illustrative materials that may be employed to form the
granules 20 include the epoxy resins containing both epoxide and
hydroxyl groups and the urethane resins resulting from reactions
between hydroxyl groups and polyisocyanates. For a more detailed
discussion of representative thermoplastic and thermosetting resins
which are useful as the granule material, reference may be had, for
example, to De Vries et al U.S. Pat. Nos. 3,171,827 and
3,254,563.
The resin material for the granules 20 is obtained commercially in
liquid, powder or pelletized form. The material is thoroughly mixed
with glass spheres having a diameter in the range of from about 6.0
microns to about 0.125 inches and an index of refraction of from
about 1.5 to about 2.0 and even higher depending upon the
particular application. For highway striping, for example, the
glass spheres may be produced from conventional soda lime silicate
glass having an index of refraction of about 1.5. For roadways in
areas subjected to heavy precipitation, or for signs, motion
picture screens and other applications where even better
reflectivity is desired, the spheres may be fabricated from some of
the titanium glasses having a higher index of refraction, or they
may comprise spheres having varying indices or spheres coated with
a reflective material such as silver or aluminum. As an
illustration, good results may be achieved where the spheres
located in the interior of the granules have an index of refraction
of, say, 1.5, and the exposed spheres on the surfaces of the
granules have an index of refraction of about 1.9.
A suitable pigment is added to the mixture of resin material and
glass spheres to impart reflection to the resin as well as color
and opacity. For edge striping on a highway, for example, a white
pigment is employed such as rutile titanium dioxide or anatase
titanium dioxide, for example. Other pigments that may be used to
produce white, yellow or other colored mixtures include aluminum
oxide, iron oxide, silicon carbide, antimony oxides, lead oxide,
lead chromates, zinc chromates, cadmium pigments, siennas, umbers,
inorganic or organic reds, chrome yellows, chrome oranges, chrome
greens, etc. The pigments can be extended with suitable natural or
manufactured granule materials.
The thermosetting resins commonly are available in liquid form.
Upon being mixed with the glass spheres 27 and the pigment, the
liquid is spread onto the upper surface of a flexible rubber sheet
or belt which contains a multiplicity of tetrahedron-shaped
indentations. A suitable doctor blade may be employed to urge the
material into each indentation. The material is then cured at an
elevated or room temperature, and the sheet is flexed to discharge
the individual tetrahedron granules into appropriate collecting
equipment. Additional spheres may be applied to the surfaces of the
tetrahedrons as they are formed, and one preferred embodiment used
spheres having a refractive index of about 1.5 in the interiors of
the tetrahedrons to provide rigidity and good wear resistance, and
surface spheres having a refractive index of about 1.9 for high
retroreflectivity.
The thermoplastic resins, on the other hand, for the most part are
available commercially in powder or pelletized form. After being
mixed with the glass spheres 27 and the pigment, the particulate
material is extruded under heat to form a softened flat sheet which
is shown by the reference character 35 in FIGS. 6-9. The sheet 35
includes a multiplicity of the glass spheres 27 substantially
evenly dispersed therein. At this stage in the manufacturing
process substantially all of the spheres are imbedded within the
resin material, and the glass is not exposed to any great extent on
the flat opposed surfaces of the sheet.
As best shown in FIG. 7, the thermoplastic sheet 35 is then
advanced between two spray nozzles 37 and 38. The nozzles 37 and 38
direct additional glass spheres 27 onto the opposed flat surfaces
of the sheet 35 to partially imbed the additional spheres in the
still tacky material.
The sheet 35 containing the glass spheres 27 dispersed therein and
on its opposed flat surfaces is advanced through the nip between
two rollers 40 and 41 (FIGS. 8 and 9). The rollers 40 and 41 are
rotated at a constant speed by a suitable drive mechanism (not
shown). The lowermost of these rollers 40 contains a multiplicity
of tetrahedron-shaped indentations 42 throughout its cylindrical
surface, and the indentations correspond in size and configuration
to the plastic granules 20a, 20b and 20c illustrated in FIGS. 3-5.
Thus, some of the indentations are of a size equal to or only
slightly greater than the large granules 20a, other indentations
are of a size equal to or only slightly greater than the medium
granules 20b, and still other indentations are of a size equal to
or only slightly greater than the small granules 20c. The
indentations serve as molds for the individual granules, and as the
sheet 35 passes between the rollers 40 and 41 the sheet material is
urged under pressure into each indentation to thereby form the
granules. The glass spheres 27 are substantially evenly dispersed
throughout each granule with some of the spheres protruding through
the outer granule surfaces.
As the thus molded granules 20 leave the nip between the rollers 40
and 41, the roller 40 is cleaned by scraping excess resin material
from its cylindrical surface through the use of a doctor blade 45.
The excess material is discharged into a trough 46 so that is may
be recycled to form additional granules.
Upon continued rotation of the roller 40, the granules 20 within
the indentations 42 drop onto a suitable conveyor 50. The conveyor
50 collects the granules 20 and transports them to a suitable
bagging machine or other packaging equipment.
The proportion of the glass spheres 27 within and on the surfaces
of each of the granules 20 should be carefully controlled to
provide optimum reflective properties. For best results the
finished granule incorporates about 30 percent to about 60 percent
by weight of the spheres. If the weight of the spheres exceeds
about 60 percent of the granule material the structural integrity
of the granules is too poor to provide a satisfactory product,
while with a sphere weight below about 30 percent of the granule
material the reflectivity is so low that the granules are
unsuitable for use as a reflective marker. In cases in which the
weight of the spheres within each granule and on its exposed
surfaces is about fifty percent the weight of the granule, the
granule exhibits particularly good characteristics when employed
for lane marking and other highway striping.
The thus prepared granules 20 are applied to a roadway or other
surface through the use of conventional delineation equipment. The
granules are dropped from a random position onto the surface, and
each granule comes to rest with one of its flat faces disposed in a
downward direction such that it is imbedded in the paint. The
different size granules 20a, 20b and 20c are evenly distributed on
the surface, and when the paint or other film forming material is
fully cured the particles are firmly held in position to provide an
extremely effective reflective marker.
In some embodiments of the invention the reflective granules 20 may
be pre-mixed with liquid paint prior to being applied to the
surface. For highway striping, for example, the mixture of paint
and granules is applied directly to the roadway, and a large
percentage of the granules become oriented with the faces 22
disposed in a downward direction while the viscosity of the paint
is still relatively low. As the pain dries and hardens, the
granules are maintained in place, and upon being exposed to traffic
the thin layer of paint adjacent the upper portions of the granules
is worn off to provide good reflectivity.
In order to more thoroughly disclose the nature of the present
invention, the following examples illustrating the invention are
given. It should be understood, however, that this is done solely
by way of example and is intended neither to delineate the scope of
the invention nor limit the ambit of the appended claims.
EXAMPLE 1
Methyl methacrylate resin in liquid form is mixed with a
conventional white highway pigment and with glass spheres
manufactured in accordance with the teachings of T. K. Wood U.S.
Pat. No. 2,945,326. The spheres are of soda lime silicate glass
with an index refraction of 1.5, and they range in diameter from
200 microns to 350 microns. The spheres are substantially evenly
dispersed throughout the resin in a proportion of about 1 part by
weight of spheres to about 2 parts by weight of the resin
material.
Through the use of a doctor blade, the thus prepared mixture is
spread over a flat rubber sheet which contains a multiplicity of
tetrahedron-shaped indentations in its upper surface. The mixture
is urged into each of the indentations and is cured through the
application of heat to form a multiplicity of tetrahedron-shaped
granules containing glass spheres substantially evenly dispersed
throughout each granule with some of the spheres protruding through
the outer faces thereof. The indentations in the sheet are of a
size such that approximately one-half of the granules have a height
of 6 millimeters and one-half have a height of 4.5 millimeters. The
granules are removed from the indentations and placed in bags.
The bags of reflective particles produced in this example are
transported to a roadway, and the particles are dropped from a
random position onto a line of moist white traffic paint having a
thickness of approximately 0.75 millimeters. Each of the particles
drops onto the paint with one of the faces of the particle disposed
in a downward direction such that is is imbedded in the paint. As
the paint dries, the particles are firmly held in position on the
roadway to provide an extremely effective reflective marker. After
repeated exposure of the roadway to heavy traffic, the upper
portions of some of the larger reflective particles are flattened
by abrasion, but substantially all of the particles remain imbedded
in the paint, and there is only a very slight decrease in
reflectivity even after extended periods of use.
EXAMPLE 2
Acrylonitrile butadiene styrene resin in powder form is mixed with
glass spheres produced in accordance with the teachings of T. K.
Wood et al U.S. Pat. No. 3,279,905. A titanium glass is used for
the spheres to provide an index of refraction of 1.9, and the
diameter of the spheres ranges between about 350 microns and about
630 microns. The resin-sphere mixture is extruded at an elevated
temperature to form a thin tacky sheet, and additional glass
spheres are sprayed onto both of the flat surfaces of the sheet to
partially imbed the additional spheres therein.
The sheet in a softened condition is then advanced through the nip
between a pair of continuously rotating rollers of the type
illustrated in FIGS. 8 and 9 of the drawings. One of the rollers is
provided with a multiplicity of indentations in its cylindrical
surface which are each in the shape of an equilateral tetrahedron.
As the sheet moves between the rollers the sheet material is urged
into these indentations to form a multiplicity of
tetrahedron-shaped thermoplastic granules containing glass spheres
substantially evenly dispersed throughout each granule with some of
the spheres protruding through the outer surfaces thereof. The
indentations in the roller are of two different sizes such that
approximately 50 percent of the tetrahedron-shaped granules have a
height of 4 millimeters and the remaining 50 percent have a height
of 6 millimeters. The weight of spheres within each granule is
equal to that of the granule material.
The granules are removed from the indentations in the roller and
are transported to a highway, where they are dropped from random
positions onto a yellow line of still tacky traffic paint along the
center of the highway. Each granule comes to rest with one of its
flat faces disposed in a downward direction and imbedded in the
paint. After the paint has dried the granules remain in position
during periods of heavy rain and after long use.
EXAMPLE 3
Polypropylene resin in pelletized form is extruded at a temperature
of 180.degree. C. to form a thin flat sheet. Glass spheres having a
size of between 50 and 100 mesh U.S. Standard are sprayed onto the
opposite faces of the sheet while the sheet is maintained in a
softened condition at about 120.degree. C. to about 140.degree. C.
The spheres are of barium titinate glass with an index of
refraction of 1.9 and are partially imbedded in the faces of the
sheet. The sheet is then advanced in a softened condition over a
roller which contains a multiplicity of tetrahedron-shaped
indentations in its cylindrical surface to urge material from the
sheet into the indentations and thereby form a multiplicity of
tetrahedron-shaped granules containing glass-spheres. The
indentations are of equal size to similarly produce equal-size
granules having a height of 4.5 millimeters. The proportion of
spheres to the polypropylene resin is about 3 parts by weight of
spheres to about 5 parts of resin.
The tetrahedron-shaped granules are transported to a highway and
dropped onto a line of tacky traffic paint in the manner described
above. Upon the hardening of the paint the granules remain in
position and exhibit good reflectivity characteristics.
EXAMPLE 4
In each of the foregoing examples a pigment of the same color as
that used for the highway line is admixed with the resin material
prior to the time the material is extruded. The resulting granules
have a corresponding color and provide a further improvement in the
reflectivity of the line.
EXAMPLE 5
A thin coating of silver is applied to the glass spheres in the
manner more fully described in copending U.S. patent application
Ser. No. 346,648 filed Feb. 8, 1982. The thus coated spheres are
used to produce plastic granules in the manner set forth in
Examples 1-4, and the granules are dropped from a random position
onto the horizontally disposed painted surface of a highway sign
while the paint is in a tacky condition. The granules remain in
place on the sign for an extended period of time and provide an
even further improvement in the overall reflectivity.
The terms and expressions which have been employed are used as
terms of description and not of limitation, and there is no
intention in the use of such terms and expressions of excluding any
equivalents of the features shown and described or portions
thereof, but it is recognized that various modifications are
possible within the scope of the invention claimed.
* * * * *